The ROR1 cell surface biomarker is expressed on B-cell Chronic Lymphocytic Leukemia (B-CLL) cells but not on healthy B-cells or other white blood cells (WBCs) in B-CLL patients. We propose to develop an inexpensive, easy-to-use, rapid, ultrasensitive assay specific for ROR1 for the detection and monitoring of B- CLL from a single drop of blood. Our goal is to attain detection levels better than currently available methods, the most sensitive flow cytometry (MRD-FC) or equal to polymerase chain reaction (ASO-PCR) methods available to detect Minimal Residual Disease (MRD). Early detection of MRD is critical in managing therapy and detecting the emergence of drug resistant malignancies. Current methods are expensive with regard to instruments, reagents, and the need for highly trained technicians. Moreover, FC methods do not adequately differentiate between B-CLL and other clonal B-cell malignancies such as mantle cell lymphoma and splenic marginal zone lymphoma. Current tests require venipuncture to collect 1-3 mLs of blood and the time to results are hours for FC and a week for ASO-PCR. JBI possesses a platform technology to address these shortcomings. JBI's first use of its technology resulted in the ZivaTM Ultrasensitive BrdU Cell Proliferation assay. Using only 50 <L of sample, Ziva detected 1-4 proliferating cells among 105 non-proliferating cells, a claim others have not approached. Applying this level of sensitivity to the detection of B-CLL would make it an attractive competitor to ASO-PCR, the most sensitive method. However, unlike ASO-PCR that takes one week to perform and is very expensive, the Ziva assay can be performed in 1 hour from a single drop of blood and is inexpensive. Together with the use of ROR1, a specific biomarker or B-CLL, if successful the resulting assay could differentiate between B-CLL and other clonal B-cell malignancies. Preliminary data show that an early-stage adaptation of our technology yielded an almost 2-fold better sensitivity than 4-color FC. We anticipate further improvements using our assay development strategies. Where standard FC methods for monitoring disease progression require 1-3 mL of blood collected by venipunture, JBI's assay proposes using a finger prick to collect a blood sample which represents a far more convenient method of sample collection for routine monitoring of patients. If successful the proposed test will be more sensitive and specific than FC and reduce the overall cost burden of patient management. Our approach focuses on three specific aims: AIM 1: To develop cell surface assay model systems using cells with known surface markers. AIM 2: To develop and optimize the analytical performance of the ROR1/CLL pilot assay using cell lines. AIM 3: To preliminarily evaluate the ROR1/CLL assay performance characteristics using clinically relevant samples.